1. Field of the invention
This invention relates to serial dilution of liquid samples and, more particularly, to a valve device for use in serial dilution of liquid samples and to a method of accomplishing such dilution.
2. Prior Art
Analysis of liquid samples is often carried out on two or more aliquots of a single sample diluted to different concentrations. Taking a blood sample, one aliquot may thus be diluted to form a first solution having a concentration of, say 1:200, while another aliquot may be diluted to form a second solution having a concentration of, say, 1:50000. In such cases, where the concentrations differ by a factor of 100 or more, the preparation of the second solution normally has to be accomplished by serial dilution, that is, by further dilution of a portion of the first solution.
Automatic apparatus for performing serial dilution of liquid samples are known in the art, U.S. Pat. Nos. 3,291,347 and 3,990,853 showing exemplary embodiments.
In the prior art apparatus, a valve device comprising a housing and a valve body movably mounted in the housing is used to isolate measured volumes of the sample and the first solution, and to effect combination of such isolated volumes with measured volumes of diluent. The valve body is provided with a pair of through passageways of precise, known volumes. In one valve body position, the passageways are filled respectively with undiluted sample and the first solution, and in a second valve body position the volumes of the sample and the first solution are expelled from the passageways into different receiving vessels and mixed with measured volumes of diluent.